This application is an improvement based upon a "Doubly-controlled Aquarium Safety Heater" of U.S. Pat. No. 5,113,057 (hereinafter designated as "prior art") also granted to the same inventor of this application.
The prior art taught an aquarium heater including a heating coil and a thermostat formed in a glass tube, a thermo-sensitive resistor remotely connected to the thermostat for ensuring a reliable sensing of water temperature in the aquarium without being thermally influenced by the heating coil, and a thermal type circuit breaker provided in a circuit of the thermostat and the heating coil for safely switching off a power supply to the heating coil once the thermostat is out of order to prevent killing of fishes raised in the aquarium.
The thermal type circuit breaker when made with bimetal strip and once sealed into the glass tube will not be adjustable. For instance, when it is intended to adjust an electrical contact pressure between the contactors of the bimetal circuit breaker, it will not be accessible from the exterior of the tube to adjust such contactors.